1. Field of the Invention
The present invention relates to a recording head for recording data on a recording medium, a recording apparatus and a recording method. More particularly, the present invention relates to an ink jet recording head for forming a liquid droplet by discharging liquid from an orifice, an ink jet recording apparatus and an ink jet recording method.
2. Related Background Art
Ink jet recording of this type is disclosed, for example, in Japanese Patent Application Laid-Open No. 54-51837. This ink jet recording applies heat energy to liquid to generate a motive force for discharging liquid droplets.
Specifically, according to this ink jet recording described in the above Application, liquid applied with heat energy is heated and bubbles are formed. A force generated by these bubbles impels a liquid droplet to discharge from an orifice formed at the top of a recording head to thereby record data on a recording medium.
A recording head used for this recording method is generally provided with: an orifice (discharge port) from which liquid is discharged; an upper protective layer for protecting a heat generating resistor element from ink, the resistor element being an electrothermal converter functioning as a means for generating heat energy to be used for discharging a liquid droplet; and a liquid discharging unit having a liquid flow path partially constituted of a heat acting part at which the heat energy for discharging a liquid droplet is applied to the liquid.
A driver element for driving such an electrothermal converter is built in the same element substrate as the converter, which is proposed in Japanese Patent Application Laid-Open No. 57-72867.
The driver element built in the element substrate is generally formed by a bipolar transistor or an NMOS transistor. Each of these transistors has some on-resistance. It is said that a variation of on-resistances of NMOS transistors is particularly large.
As described in Japanese Patent Application No. 5-223495, for the correction of energy to be applied to an electrothermal converter to compensate for a variation of each sheet resistance of a heat generating resistor layer constituting the electrothermal converter, a detector for detecting a sheet resistance is formed on an element substrate on which the electrothermal converter is formed. The detected information is picked up from the head to change the conditions, e.g., a pulse width of a signal input to the head from the printer. With this correction, energy applied to the electrothermal converter is made constant.
The amount of energy applied to an electrothermal converter greatly influences the printing performance and durability. The printing performance becomes better as the energy is increased more. From the viewpoint of the printing durability, it is required to lower the energy amount in order to prevent breakage of the electrothermal converter. A liquid droplet smaller than that conventionally used is required to be discharged, as the recording density and precision become higher. The printing performance is therefore required to be considered more than conventional.
In order to improve ecological effects, a cartridge with an integrated head and ink tank is now changing to a separation type of a head and ink tank so that the head can be used during a longer period by replacing only the ink tank. In this connection, the durability of a head becomes more important than conventional.
From the above reason, it is necessary to precisely control the amount of energy to be applied to an electrothermal converter.
However, as described earlier, the drive element for driving an electrothermal converter has some on-resistance which varies depending upon drive element manufacture processes. Even if the same voltage is applied to a head, the voltage applied across electrothermal converters becomes different if on-resistances are different. In this case, the printing performance changes with each head, and heads with bad printing performance may appear. Apart from this, electrothermal converters of some heads may become non-conductive.
NMOS transistors in particular have a large variation of on-resistances although manufacture processes of driver elements are simple and the cost can be reduced. The above problems may possibly occur therefore when NMOS transistors are used for drive elements.
If the drive conditions are properly set in accordance with the measured on-resistance of each head before it is shipped, the above problems can be avoided. However, in the case of a head of the type replaceable by a user, a user is required to set the drive conditions each time the head is changed.
In order to solve the above problems, a recording head of this invention comprises: a heat generating resistor layer and an electrode layer formed on an element substrate, the heat generating resistor layer and the electrode layer constituting an electrothermal converter for generating heat energy; a driver element built in the element substrate for driving the electrothermal converter; and an element built in the element substrate for detecting the characteristics of the driver element.
The recording head as above may further comprise an ink flow path disposed with the electrothermal converter, the ink flow path including a heat acting unit communicating with an ink discharge port and generating bubbles in liquid by supplying the liquid with heat energy.
A recording apparatus for recording data on a recording medium comprises: the recording head as described above; and means for transporting the recording medium on which data is recorded by the recording head.
A recording method for recording data on a recording medium comprises the steps of: providing a recording head including an electrothermal converter to be used for recording, a driver element for driving the electrothermal converter, and driver element characteristics detecting means for detecting the characteristics of the driver element; detecting the characteristics of the driver element with the driver element characteristics detecting means; and changing the drive conditions of the electrothermal converter in accordance with the detection results of the driver element characteristics detecting means.